Credit value: 5 2Energy and our Universe - Pearson Education · PDF fileAssessment and grading...

Credit value: 5

Learning outcomesAfter completing this unit, you should:

1 be able to investigate how various types of energy are transformed

2 know applications of waves and radiation

3 know how electrical power can be transferred for various uses

4 know the components of the Solar System and the way the Universe is changing.

Most of the appliances we use at home and at work use energy from

sources that are running out. If we are not careful we won’t have any energy

to do the things that we take for granted. By understanding energy better,

we can plan for the future by designing and building new technology that

lets us derive energy from sources that will not run out.

In this unit you will learn how energy is transferred and used along with the different sources of energy and how they can be used to generate electricity. You will investigate how we can make better use of the energy we use at home and in the workplace. You will also have the opportunity to carry out practical work, for example investigating how to minimise energy loss at home.

You will also learn about different types of light and radiation and how they can be used in our everyday lives and in the world of work, such as the use of gamma radiation to treat cancer patients.

Finally you will learn about the Universe and our place in it. You will have the opportunity to investigate the origin of the Universe and our Solar System and discover theories that astronomers have to explain how the Universe is changing.

2 Energy and our Universe

BTEC’s own resources

36

Assessment and grading criteria This table shows you what you must do in order to achieve a pass, merit or distinction grade,

and where you can find activities in this book to help you.

To achieve a pass grade the evidence

must show that the learner is able to:

To achieve a merit grade the evidence

must show that, in addition to the pass

criteria, the learner is able to:

To achieve a distinction grade the

evidence must show that, in addition to

the pass and merit criteria, the learner

is able to:

Carry out practical investigations that

demonstrate how various types of

energy can be transformed

See Assessment activities 2.1, 2.2,

2.3 and 2.4

Describe the energy transformations

and the efficiency of the

transformation process in

these investigations

See Assessment activity 2.2

Explain how energy losses due to

energy transformations in the home

or workplace can be minimised

to reduce the impact on the

environment


Calculate the efficiency of energy

transformations


Describe the electromagnetic

spectrum


Describe the uses of ionising and

non-ionising radiation in the home

or workplace


Discuss the possible negative effects

of ionising and non-ionising radiation


Describe the different types of

radiation, including non-ionising and

ionising radiation


Describe how waves can be used for

communication


Explain the advantages of wireless

communication


Compare wired and wireless

communication systems


Describe how electricity can

be produced

See Assessment activities 2.9, 2.10

and 2.11

Compare the efficiency of electricity

generated from different sources

See Assessment activities 2.11

and 2.12

Assess how to minimise energy losses

when transmitting electricity and when

converting it into other forms for

consumer applications


Describe how electrical energy

is transferred to the home

or industry


Describe the use of measuring

instruments to check values predicted

by Ohm’s law in given electric circuits


Describe the composition of the

solar system


Describe the main theory of how the

universe was formed


Evaluate the main theory of how the

universe was formed


Identify evidence that shows how the

universe is changing


Explain how the evidence shows that

the universe is changing


Evaluate the evidence that shows how

the universe is changing


P1 M1 D1

P2

P3

P4

M2 D2

P5

P6

P7

P8

M3

M4

D3

D4

P9

P10

M5

M6

D5

D6

How you will be assessedYour assessment could be in the form of:

presentations

case studies

practical tasks

written assignments.

Unit 2 Energy and our Universe

37

Tariq, 18 years oldI enjoyed this unit and I particularly liked the section on the Solar

System as looking at the night sky fascinates me. It is amazing

how we can see objects that are millions of miles away from us.

Our class took a trip to the National Space Centre, in Leicester,

which was fantastic and it brought this unit together.

I found the section on using light in communication very useful as

it showed me that there are lots of technologies, some better than others. We

experimented with laser light, which I found really interesting.

Energy issues are always on the news and the section on energy allowed me to be

part of this debate. I feel that completing this unit has improved my practical skills

and made me more aware of the world we live in.

Have you got the energy?Imagine our lives without energy. How could we work without eating or drinking? How could a bus move from one bus stop to another without the fuel its engine needs? How could your mp3 player work without the electrical energy it requires to power it up?

In small groups discuss some other things you have used recently that require energy. In your groups work out what type of energy has been used.

Catalyst

2.1 Understanding types of energyTypes of energyEnergy is vital to everyday life and we use it to do all sorts of things. The

table below shows some examples of different types of energy.

Type of energy What is it? Example

Potential (e.g.

elastic, gravitational,

chemical)

Stored energy that has

the potential of doing

work

Kinetic Movement energy

Light

(electromagnetic)

Bright objects give out

light energy

Sound Things that vibrate

give off sound energy

Thermal (heat) Energy that is

transferred from a

hot region to a cold

region

Electrical Flow of charge in an

electric circuit


Grading tip

Part of meeting the criteria is to

list types of energy. When doing your

assignment, make sure you give all

the different types of energy given in

the table.

In this section:

Sound energy is used to test metals in the aerospace and automotive industries. Cracks, or weak areas, refl ect the energy.

38

P1

P1

39


Energy transformationsWe need energy to do all sorts of things. Running, reading and even

sleeping require energy. Energy can be transformed (changed) from

one form to another. Anything that takes in energy must also give out

energy. Here are some examples.

A girl running gets her energy from the food she eats. The energy

is then transformed to movement (kinetic energy), sound and

heat energy.

The light bulb that lights your room gets its energy from electricity.

The energy is then transformed to light and heat energy. Remember:

don’t touch a lit bulb – it will burn.

You are a food scientist working for a supermarket, looking at energy in food.

1 Find out how much energy is stored in a can of drink (any type). This value will be marked clearly on the label.

2 What form of energy is in this drink?

3 Investigate what happens to this drink as it goes into your body.

Grading tipRemember, everything requires energy – even sleep! This means that you should be able to find enough types of energy to cover the content for .

Assessment activity 2.1

Using energy at home and in the workplaceWe use many different appliances at home and at work that convert

energy from one form into others.

Activity A

Write down three ways in which you have experienced energy being transformed today.

Activity B

For each thing pictured on the right, write down the type of energy that is going into it and the types of energy that it is giving out. (Hint: remember that most things give out more than one form of energy.) Energy transformations

are all around us.

PLTS

When you carry out your investigation you will be learning to enquire independently as well as developing your self-management skills.

P1

P1P1

P1

P1

2.2 Describing energy

Electrical energy used

for radio, lights,

recharging battery etc.

Kinetic energy

used to move

the lorry

Chemical energy

from burning

fuel

Wasted thermal

(heat) and sound

energy

An energy block diagram showing the energy transfers that occur in a moving lorry.

40


In this section:When engineers and designers create the appliances we use in

everyday life they need to know how much energy is transformed to

useful forms and how much is wasted. They can then improve their

designs by trying to reduce the amount of wasted energy. For instance,

we now have more effi cient ‘energy-saving’ light bulbs in our homes.

Case study: Energy-effi cient fl ight

Jenny is a trainee engineer working for an aerospace company. She is working with other engineers to design a more effi cient engine for the planes. They want the engine to transform as much energy as possible into useful forms and to reduce the amount of energy that is wasted.

Which types of energy given out by the engine are wasted?

Investigating energyYou need to be able to describe energy changes that take place in

everyday situations. It is helpful to break the problem down. This

example shows you how you could do this:

Consider a ball on a work bench. What kind of energy does the ball

have? (Hint: what energy is related to having the potential to do

something?)

Now consider what happens as the ball falls. What energy is being

transformed? (Hint: which energy is related to motion?)

As the ball hits the ground and then rebounds, does it reach the

height it fell from? Explain your answer in terms of how energy is

transformed.

Tracking transformationsWe use energy block diagrams

to understand how energy

is transformed. This block

diagram shows the energy

transfers that occur

in a moving lorry.

Energy block diagram – shows the

forms of energy going into and out of

a system.

Sankey diagram – shows how much

energy is going into and out of a system.

Conservation of energy – tells us that

energy is transformed to various forms

and is not destroyed.

Key terms

Engineers design aeroplanes to be as energy effi cient as possible.

M1P1

Chemical energy

from burning fuel

200 000 J

Wasted thermal (heat)

and sound energy 100 000 J

Kinetic energy used to move the lorry

80 000 J

Electrical energy used for radio, lights,

recharging battery etc. 20 000 J

A Sankey diagram showing the size of the energy transfers for a moving lorry.

41


The block diagram shows you that the lorry is powered by chemical

energy in the form of fuel. The chemical energy is transformed into:

kinetic energy that moves the lorry

electrical energy that powers the lights, radio, recharges the battery etc.

sound energy

thermal (heat) energy.

The heat and sound energy are transferred to the surroundings as

wasted energy.

Useful versus wasteful energyIt is useful to know how much energy is actually transferred

into useful energy and how much into wasteful energy.

You can show this by constructing a different type of block

diagram called a Sankey diagram. A Sankey diagram for

the moving lorry is shown on the right.

In a Sankey diagram the energy flow is shown by arrows.

Broad arrows show large energy transfers. Narrow arrows

indicate small energy transfers. We say that the width of

the arrow is proportional to the energy.

The total amount of energy that comes out of the lorry is

equal to the total amount of energy that goes in. We say

that the energy is conserved. Physicists call this the law of

conservation of energy.

You are working for a leading IT company. Your manager wants you to look into energy-efficient computers. To start, you investigate the energy used by one of the company’s existing computers.

1 State in words the types of energy involved when the computer is in use.

2 Draw a block diagram to show the energy transformations.

3 350 J of electrical energy is supplied to the computer. In the process 65 J is used to generate light energy, 190 J is transformed into thermal (heat) energy and 95 J is transformed into sound energy.

Draw a Sankey diagram to show the energy transfers.


M1

M1

P1

M1P1

Activity A

Draw a block diagram to show the energy transformations for someone using a hairdryer. (Hint: energy comes out of the hair dryer in more than one form.)

Grading tipRemember that when you draw a Sankey diagram, the amount of energy leaving the system must be the same as the energy that enters it.

2.3 Understanding thermal energyIn this section:

Free electrons – electrons within the

atom of a metal that are shielded from

the nucleus and are free to move.

Density – the amount of matter that

occupies a specifi c volume; something

heavy that takes up a small space

has a higher density than something

that weighs the same but takes up

more space.

Key terms

Vacuum fl asks keep liquids hot by minimising heat loss due to conduction, convection and radiation.

When you touch a metal gate on a winter morning it feels cold. This is

because the thermal (heat) energy from your hand is being transferred

to the metal.

Scientists need to understand how thermal energy is transferred so that

they can design useful products. For example, a vacuum fl ask is used

to keep liquids hot (or cold) by preventing heat transfer. Saucepans are

made out of stainless steel so that they transfer heat quickly from the

cooker to the food inside the pan.

Thermal energy can be transferred in three ways: conduction,

convection and radiation.

ConductionYou know that all substances consist of atoms. In a solid, the atoms are

close together; in a liquid, the atoms are more spread out; and in a gas,

they are very far apart.

Unit 1: Page 6 shows the structures of solids, liquids and gases.

The atoms in substances vibrate. When a substance is heated, its

atoms vibrate more. If one end of a metal bar is heated, the other end

eventually gets hot. You may have noticed this if you’ve used a metal

spoon in a saucepan. This is because the heat is transferred from atom

to atom through vibrations; this is called conduction. Solids conduct

thermal energy better than liquids or gases because the atoms are

closer together in solids. Metals are the best conductors of heat

because they also have free electrons that transfer thermal energy.

HEAT

free electrons

A non-metal transfers heat through the vibration of its atoms. These are poor conductors of heat but good insulators.

A metal transfers heat through the movement of free electrons as well as through the vibration of its atoms.

HEAT

42


P1

The warm air is less

dense so risesAs the air

cools down

it becomes

more dense

and sinks

The radiator heats

the air surrounding it

Cool air moves in

to replace the warm air

Activity A

Imagine heating up some baked beans in a metal saucepan. You stir the beans with a metal spoon. Using the idea of conduction, explain why the spoon gets hot.

Activity B

Now imagine heating up some soup. Even if you don’t stir it the whole pan of soup eventually heats up. Use the idea of convection to explain why.

ConvectionThe atoms in liquids and gases are free to move around because they

are joined by only weak forces. Thermal energy can be transferred

because of the movement of these atoms. This is called convection.

Convection allows a radiator to heat a whole room rather than just the

air immediately surrounding it. This is shown in the diagram on the right.

This room is being heated by a radiator; the convection current is shown by arrows.

43


RadiationRadiation is the third way of transferring thermal energy. The heat is

transferred by infrared light waves. It does not involve atoms. Radiation

is absorbed by dark dull objects and is reflected by shiny substances

such as metals. You may have seen an athlete wrapped in a shiny

blanket after a race – this prevents the body temperature from dropping

too quickly.

Unit 2: You can learn more about radiation on page 45.

Did you know?

The warmth that we get from the Sun is from infrared radiation, coming from the Sun almost 92 million miles away.

1 Explain why the whole of a pan of soup gets hot, even if you don’t stir it.

2 Work in groups of three. Produce a leaflet showing different ways that we use heat transfer in the home and the workplace.

Grading tipRemember that solids transfer thermal energy by conduction and liquids and gases by convection. Radiation is light and doesn’t need a medium to transfer thermal energy.

PLTS

Producing the leaflet in your groups will help you develop team-working and self-management skills

Assessment activity 2.3 P1

P1

P1

Grading tip

Loft insulation

prevents heat

loss through the

roof by conduction

and convection

Silver foil behind

radiators prevents

heat loss by

radiation as does

painting walls white

Carpets on

floors prevent

heat loss by

conduction

Cavity walls filled with foam

prevents heat loss through

the walls by conduction and

convection. Metal foil can

reflect radiation.

Draught proofing in doors and

windows and curtains prevent

heat loss by convection

Double glazing

in windows

prevents

heat loss by

convection

Methods of insulating a house.

Background photo

to come

D1

1 Investigate your own house. List the methods that are used to minimise energy loss.

2 What else might you do to minimise energy loss from your house?


44


2.4 Catch that energy

The red areas in this thermal image of a house show where most heat energy is being lost.

The cost of energy is going up and our non-renewable energy resources

are going down. Minimising loss of energy is becoming important for

all of us. Also, in generating the energy that we use, carbon dioxide gas

is given off, which is thought to be responsible for making the Earth

warmer. This means that reducing energy loss is good not only for our

pockets but also for our planet.

Activity A

Look at the thermal image of the house. Identify which areas of the house are losing energy.

In this section:

Heat is lost from our houses mostly through the walls and roof, and to a

lesser extent through the doors, fl oor and windows. The diagram below

shows how energy can be saved.

Remember that the criteria ,

and need to relate to each

other. So when you are planning the

investigation , make sure that it

relates to minimising energy in the

home or workplace. Make sure you

include experiments on conduction,

convection and radiation.

D1M1P1

P1

M1 D1

P1 D1

D1

D1P1

P1

Principal Manufacturing Engineer, Astrium Ltd

The best thing about the job

I like working with end-products which will actually go into Space. I enjoy my work because it can affect our everyday lives. Our satellites can help

climatologists better understand our environment by observing climate change, or can help improve global communications and the quality of television broadcasts from space.

ScenarioOur work has to meet high standards set by external bodies such as the European Space Agency.

When we make electronic circuits we use very thin gold wires to electrically connect microchips to the rest of the circuit. These wires are thinner than human hair but have to be strong

enough to survive huge forces and vibrations during rocket launch once the circuit is inside a satellite.

Each wire is tested by pulling it with a special machine to make sure that it won’t break.

Kevin Wright

I am an engineer working in the UK’s Space Industry and I’m involved with production

of electronic circuits which will be fi tted in a satellite to work in Space.

My responsibilities include:

electronic circuits, including instructions on using equipment safely

(Control of Substances Hazardous to Health). We have to tell people if a material is hazardous and what to do if they come into contact with it

necessary for them to be used in space.

Think about it!

A new machine arrives from America but is only wired to connect to their 120 V mains supply. What would you do?

You have installed a new component cleaning process but the chemical it needs doesn’t have a COSHH certifi cate. What would you do?

WorkSpace

45

P3 P5 M3 D3

energy input

useful energy

output

46


2.5 Effi ciencyIn this section:

Input – the energy that goes into a

system.

Output – the energy that goes out of

the system.

Tungsten fi lament light bulb – the

standard type of light bulb in which

the fi lament (the tightly curled

wire that glows) is made out of the

metal tungsten.

Key terms

Energy-saving bulbs waste up to 75% less energy through heat than standard tungsten fi lament light bulbs.

Often, a lot of the energy that goes into a system is wasted, mainly

as heat. To save energy and money, electronics manufacturers are

developing appliances that make better use of energy and therefore

waste less. We describe these as energy effi cient. One successful

example is the energy-saving light bulb.

The energy that is usefully used by an appliance is given by the

effi ciency, which we can calculate using this equation:

effi ciency = useful energy output from the system

× 100%total energy input to the system

The effi ciency is usually given as a percentage, so it varies from 0 to

100%. Maximum effi ciency is indicated by 100%, meaning that all the

energy input is converted to useful energy output.

For example, petrol engines in cars transfer only 30% of the chemical

energy in the fuel to kinetic energy used to move the car. Electric cars

are more effi cient.

Activity A

Write down the ways in which a petrol-engine car wastes energy.

Worked exampleThe energy input per second to a desk lamp with a standard tungsten fi lament light bulb is 100 J and the output light energy (useful energy) is 5 J. Energy expressed as joules per second is actually the power, which has the unit of watts and the symbol W.

How effi cient is the lamp? Give your answer as a percentage.

Using the equation above:

effi ciency = 5

× 100% = 5%100

This lamp is only 5% effi cient. Where do you think the other 95% of the energy goes?

M4P2

Activity B

Work out the effi ciency of a fl uorescent lamp if the useful energy given out each second is 60 J. Assume that it has the same energy input as the tungsten fi lament lamp of 100 J.

Which is more effi cient?

47


Did you know?

UK businesses waste £8.5 billion worth of energy every year.

Saving our world’s energy resources There are many sources of energy. They can be divided into two types:

renewable and non-renewable. Renewable energy sources are sources

that will never run out. Non-renewable energy sources cannot be

replaced once they have been used.

Type Source Energy Uses

Non-

renewable

Fossil fuels

(remains of dead

plants and animals

that died millions

of years ago)

Thermal energy

obtained by

burning oil, natural

gas and coal

Powering vehicles,

heating homes,

generating

electricity

Non-

renewable

Nuclear Thermal energy

given off during

the splitting of

atoms

Generating

electricity

Renewable Wind Kinetic energy

transferred to wind

turbines

Generating

electricity

Renewable Biofuels Crops are

fermented to

make ethanol. This

is burned to give

thermal energy

Powering cars

Renewable Sun Thermal energy

captured by solar

panels

Heating water in

homes, generating

electricity

1 An electricity company has designed a power station using the potential energy in water from hill reservoirs. The average input is 800 MW and the average output is 200 MW. What is the efficiency?

You are a member of a committee set up by the government to investigate options for different energy sources.

2 Work in groups of four with each person choosing a different energy source. Then undertake research to find out the efficiency, cost, amount of energy that can be produced and the advantages/disadvantages of each energy source.

3 Present your findings to the rest of the group, then discuss which energy sources are most suitable to meet the country’s energy needs.

4 Produce a leaflet that outlines your recommendations with the reasons why.

Assessment activity 2.5 Functional skills

You could use your ICT skills when making your leaflet.

Grading tip

To meet you will need to

calculate the efficiency of the energy

transformations you investigate in

. Remember that the useful

energy output will always be less than

the input energy.

Energy assessors calculate an energy rating of your home – you need this if you want to sell.

P2

M4

M4

P2

P1

M4

M4P2

amplitude

equilibrium

position

wavelength/period

48


2.6 Understanding wavesIn this section:

Displacement – how far the wave is

disturbed from its rest position.

Oscillation – a complete to and fro

movement; this could be going up and

down, or sideways.

Key terms

A beach is an obvious place to see waves in the sea. But this isn’t the

only place you’ll find waves – they are all around us. You are using waves

to read this sentence. Light waves are reflected from the book into

the retinas of your eyes, where the information is turned into electrical

signals which are sent to your brain from your eyes. Sound waves carry

music from a radio to your ears.

Activity A

List three examples of waves that you have used today.

What is a wave?The diagram on the left shows a wave. The properties of a wave are

described using the terms amplitude, wavelength, frequency, period

and speed.

The amplitude of a wave is the maximum displacement from its fixed

position. This is also called its equilibrium position. The wavelength of

the wave is the distance between two identical points on the wave as it

repeats itself. The period is the time for one complete oscillation.

Frequency and speedThe frequency of a wave is the number of complete oscillations it makes

in one second. The unit of frequency is the hertz (Hz). Because many

waves oscillate very quickly, frequency is often given in kilohertz (kHz),

which means 1000 waves in one second, or even megahertz (MHz),

which means one million waves in one second.

We are surrounded by waves, but mostly invisible ones. What other waves can you think of?

Diagram of wave showing amplitude, wavelength and period.

P3

49


Worked example

The frequency of microwaves used by a microwave oven is 2000 MHz. What is the period of the microwaves?

First remember to change the frequency prefix to a standard number. 2000 MHz is 2000000000 Hz.

period = 1

frequency =

1(2000000000)

period = 0.5 × 10−9 seconds (half of a billionth of a second)

The speed of a wave, which is how quickly it travels along, depends on

both the frequency and wavelength. It is given by the equation:

speed = wavelength × frequency

The speed will be in metres per second (m/s), wavelength in metres (m)

and frequency in hertz (Hz).

Did you know?

Light travels at a speed of approximately 300 million metres per second. This value is true for all types of light. We write this as 3 × 108 m/s. Sound waves are much slower – in air they travel at about 330 m/s.

1 In groups, discuss how you could model the movement of a wave.

2 Construct your model or role play it to the other groups.

Grading tipRemember that the longer the wavelength the smaller the frequency. When calculating the speed, make sure that you change the prefixes (e.g. the ‘M’ in MHz) to numbers, otherwise your answers will be wrong!


Case study: Keep your distance

Alan works as an engineer for a car company. He is helping to design a safety system that uses light waves to work out how far away the car in front is. If you are too close to the car in front, the system slows your car down automatically. In an emergency it would automatically apply the brakes for you.

Can you think of another situation in which this technology would be useful?

The frequency and period of a wave are related by the equation:

period = 1

frequency

so the period decreases as the frequency increases.

Light can be used to sense the distance between a car and other objects.

P3

P3P3

Vinfra

red

ultra

violet (uv)

gamma

rays

radio

wavesmicrowaves X-rays

low energy

Used for

receiving satellite

signals and for

cooking.

Used for TV and

radio, and for picking

up signals from

deep space.

Invisible to the

human eye, used by

TVs, DVD players,

mobile phones etc.

Given off by the Sun.

Long exposure can

cause skin cancer,

but UV light can

be useful too.

Can be dangerous

to the human body.

Used to take images

of bones.

Can be dangerous

to the human body.

Used to treat cancer.

Visible light:

the shortest wavelength

our eyes can see is violet

(410nm) and the longest

is red (710nm).

high energyhigh energyIncreasing Frequency

Increasing Wavelength

50


2.7 Understanding theelectromagnetic spectrum

Electromagnetic spectrum – the

different types of electromagnetic

radiation, arranged in the order of

frequency and wavelength, from radio

waves to gamma rays.

Key term

The electromagnetic spectrumElectromagnetic radiation is a wave. The colours of the rainbow are just

the small range of radiation that our eyes can detect as visible light.

Electromagnetic radiation outside this range is invisible to humans.

All of the different wavelengths and frequencies of radiation, from

radio waves, through visible light to X-rays and gamma rays, form the

electromagnetic spectrum.

The electromagnetic spectrum and some of its applications.

Activity A

Put these types of electromagnetic radiation in order of increasing wavelength: visible green light, X-rays, microwaves, ultraviolet.

Activity B

Give one application each for microwaves, gamma rays and infrared light.

Visible light is measured in nanometres. A nanometre is a billionth of a

metre. All radiation that makes up the electromagnetic spectrum travels

at a speed of about 300 million metres per second.

Understanding waves in communicationMany electronic devices use electromagnetic waves in some way. Some

require wires to work, some don’t. The table on the next page shows

some examples of wireless and wired communication.

The colours of a rainbow are just a small part of the electromagnetic spectrum.

In this section:

P3 P5 M3 D3

51


Did you know?

The honey bee can see ultraviolet light. Snakes such as the viper can see infrared.

You have just started work as a salesperson at a telecommunication company. You are researching the market.

1 Find out which parts of the electromagnetic spectrum are used for communications.

2 Think of two types of communication devices that you have used today that rely on electromagnetic radiation to work.

3 Working in pairs, one of you should take the role of trying to sell ‘with-wire’ technology, using a specific example from the table. The other should try to sell wireless technology, using a different example. After the role play summarise what you have found out by writing an advert.


Method of

transmission

Examples Advantages Disadvantages

Wires Cable TV, Internet

and phone calls;

infrared is sent

through optical

fibres

Excellent picture

quality

Can only be

intercepted by

physical access

Difficult to use as

and where you

want

Cables must be

laid

Wireless Wireless

keyboards, mice

and remote

controls; all using

infrared

TV and games

consoles can be

controlled from a

distance

Keyboards/mice

can be placed in

a suitable place

without having to

rearrange wires

Phones, keyboards,

mice: heavy battery

use

Wireless phones,

laptops; all using

radio waves

Laptops can be

used in different

parts of the house

Laptops: signals

can be intercepted

remotely

Wireless Satellite; use of

microwaves to

transmit TV and

mobile phone

communication

Can cover large

distances

Can carry a lot of

TV stations;

TV, radio and

Internet can be

accessed in remote

areas

There is a delay in

communication

Very expensive to

set up

Grading tip

In order to meet , make sure

that you can describe all the areas

of the spectrum that are covered on

these pages. To meet you need

to describe both wireless and wired

communication.

Communication:(a) cable using optical fibres, (b) satellite dish, (c) Wi-Fi wireless connection.

(a)

(b)

(c)

P5

M3 D3

D3M3P5

P3

P5

P5

52


2.8 Understanding radiationIn this section:

Nucleus – the inner part of the atom,

where protons and neutrons are found.

Radiation – energy spreading out, as

carried by electromagnetic radiation, or

carried by a particle.

Ionising radiation – radiation that can

remove electrons from atoms, causing

the atom to become positively charged.

Non-ionising radiation – radiation that

does not remove electrons from atoms,

e.g. microwaves or infrared.

Key terms

A stable nucleus has the right number of protons and neutrons so it

does not break apart. If the number of protons and neutrons changes,

the nucleus becomes unstable and emits ionising radiation. This

radiation has three types: alpha, beta and gamma. They differ in how

ionising and how penetrating they are, and how they react to magnetic

or electrical fi elds.

Non-ionising radiation is radiation from the low frequency end of the

electromagnetic spectrum: radio, microwave, infrared and visible light.

Alpha ( ) radiationAlpha radiation consists of particles. These are helium nuclei, each

having two protons and two neutrons, and a charge of +2. When

particles hit another substance, e.g. air, they knock electrons off the

particles they hit. This leaves the particles with a positive charge; the

particles have been ionised. Alpha radiation is highly ionising. (If you

swallow particles, they cause serious damage because they ionise

DNA.)

particles are large compared with electrons and protons so they

cannot penetrate far into a material. For example, a few centimetres

of air or a sheet of paper will stop particles. particles are weaklypenetrating. This means there is little chance of particles getting

into the human body through the skin.

Because particles have a positive charge, they will be attracted to a

negatively charged plate.

Activity A

Describe alpha radiation.

Beta ( ) radiation Beta radiation consists of fast-moving electrons that have been given off

(emitted) by unstable nuclei. If they collide with an atom, they can knock

off an electron and ionise the atom. Because particles are small, they

don’t ionise as much as particles. They are moderately ionising.

Because they are less strongly ionising, particles can travel

further than particles. They can travel through a few millimetres

of aluminium before they are stopped. They are moderatelypenetrating. This makes them dangerous if they come into contact

with living things.

Because particles are electrons, which have a negative charge,

they will be attracted to a positively charged metal plate. They are

defl ected more than particles because they are lighter.

When we think of radiation, we usually think of things like nuclear bombs and radiation leaks, which are uncontrolled radiation and are extremely dangerous. However, medical physicists can use controlled radiation to kill cancer cells in tumours.

D2M2P4

positive plate

negative plate

leadaluminium

53


Safety and hazards

We are exposed to tiny doses of radiation in our everyday lives. This is called background radiation. Some of this radiation comes from the food we eat, in the form of radioactive potassium.

Wherever there is a danger of being exposed to higher levels of radiation, especially in the workplace, you will see this symbol.

Gamma ( ) radiationGamma radiation is high-energy electromagnetic radiation. It has a very

short wavelength and is emitted from unstable nuclei.

Electromagnetic radiation does not have charge so it is difficult for

radiation to ionise particles. But because it has very high energy it

can still ionise matter. It is weakly ionising.

Because radiation is weakly ionising it can travel large distances. It

can pass through aluminium and even several centimetres of lead.

It is highly penetrating. This means that radiation is extremely

dangerous, both outside and inside the human body.

Because it does not have a charge, it is not deflected by electric or

magnetic fields.

Using ionising radiation Alpha radiation is used in smoke alarms. A weak alpha source ionises

the air and causes a small current to flow. If smoke gets into the

detector, the current reduces and the alarm sounds.

Beta radiation is used to control the thickness of paper during

production in a paper mill. A Geiger counter measures how much

radiation passes through the paper. This is used to control the pressure

on the rollers that the paper passes through.

Gamma radiation is used to kill bacteria in food so that the food does

not go bad. It is also used in the treatment of cancer.

The effect of an electric field on , and radiation.

Penetration of , and radiation.

You are working for a science charity to produce a poster or presentation on radiation.

1 Describe two properties each of , and radiation and give an application of each.

2 Describe the applications and dangers of radiation. One of you should investigate applications and the other should investigate the possible dangers in using these applications. Use a computer to prepare a poster or some presentation slides.

Assessment activity 2.8 Grading tip

For P4 , make sure you can describe

the nature of the different types

of radiation and their absorption

properties. For M2, don’t forget to

include applications of non-ionising

radiation (pages 50–51). To get

D2 , make sure that you relate the ill

effects to each type of ionising and

non-ionising radiation.

D2

P4

M2 D2

M2P4

Activity B

Describe three useful applications of radiation.

batteryswitch

resistor

bulb

voltmeter

ammeterA

V

Series circuit.

54


2.9 Understanding electricityIn this section:

Series – in a series circuit the

components are connected in a line,

end to end, so that current flows

through all of them one after the other.

Parallel – in a parallel circuit the

components are in separate paths and

the current is split between the paths.

Key terms

What is electricity?Electricity is the flow of electrical charge. The charge could be positive

and negative ions, as inside the battery of your mobile phone, or

negatively charged electrons, as in the wire of your DVD player. When

charge flows we say there is a current. Electrical energy allows a current

to flow in a circuit. For example, when your DVD player is connected to

the mains, it forms a circuit. A measure of the energy carried between

two points in a circuit is called voltage or potential difference (pd).

The two points could be each end of the bulb in the circuit shown.

An electric circuit diagram of a bulb, switch, fixed resistor, voltmeter and ammeter.

Parallel circuit.

We use a voltmeter to measure voltage and an ammeter to measure

current. The way we connect the meters is important. A voltmeter is

always connected in parallel. An ammeter is connected in series. The

picture above shows a typical circuit diagram of a light bulb with the

symbols of the different components.

Case study: Fault finder

Sophia is a technician at an electronics company. Today she is repairing a DVD player that seems to have no power. She wants to measure the voltage and find out if there is a break in the circuit.

How could she do this?

Imagine your world without electricity: no lights, no television, no central heating, no shower. It would be a strange place.

P8P6

55


Ohm’s lawOhm’s law describes how a current and voltage behave in metals. This

law can be written as:

voltage = current × resistance

V = I × R

In a practical you can use an ammeter and a voltmeter to check the

values you calculate for a circuit using Ohm’s law.

High levels of current can be dangerous. In the laboratory we use only low

levels such as a thousandth of an amp (mA) or a millionth of an amp (MA).

All electrical devices, such as televisions, hairdryers and light bulbs, have

resistors. These limit the current that flows through the components, as

they could be damaged if too much current flows through them.

Safety and hazards

Electrical current is dangerous as it could cause the heart to stop working. You can also get burns from where the current enters and leaves the body. Before working with electrical equipment make sure you ask for a safety briefing from your supervisor.

Electrical

property

Unit Symbol

Voltage volt V

Current ampere or

amp

A

Resistance ohm (Greek

symbol

omega)

Table: Units and symbols of electrical properties

Worked example

1 What is the voltage across a 300W speaker if the current flowing is 0.01A?


= 0.01 × 300 = 3V

2 If the voltage across the speaker was 9V, what current would be flowing?


so current =voltage

resistance

=9

300= 0.03A

Grading tip

Make sure that when you perform

electrical calculations you change the

prefix (e.g. ‘m’ in mA) to numbers.

You are an electrician. Part of your work is to make sure that electrical circuits are working correctly. To do this you must understand Ohm’s law and how to use measuring instruments.

1 Draw the symbols for a voltmeter and an ammeter.

2 This question uses Ohm’s law. If a resistor in a circuit is 1500Ω,what is the current through it if it is connected across a 1.5Vsupply?

3 Using a circuit diagram, show how you could confirm the current and voltage readings in question 2 by using the correct measuring instruments.


Functional skills

Correctly obtaining the value of the current involves identifying the problem and selecting the correct mathematical method.

P6

P6

P8

P8P6

Activity A

What meter is used to measure current? How should the meter be connected in order to measure the current through the circuit? Draw a diagram to show this.

(a)

(b)

56


2.10 Producing electricalenergy – batteriesIn this section:

You have probably used something powered by a battery today – your alarm clock or watch, mp3 player or a remote control.

Did you know?

A battery produces electricity by the chemical reactions that take place inside it. The chemical inside a battery is called an electrolyte. Batteries can be rechargeable or non-rechargeable.

If you look at a battery you will see two terminals. One is a positive

terminal, called the anode. The other is a negative terminal, called the

cathode. In some batteries, such as AA, C and D batteries, the ends

form the terminals.

Table: Examples of different types of batteries and where we use them.

Appliance Battery material Battery type

Mobile phone Lithium ion Rechargeable

Modern car Lithium acid Rechargeable

Very old car Lead acid Rechargeable

Laptop Lithium ion Rechargeable

Television remote

control

Alkaline Non-rechargeable

Watch Lithium-iodide Non-rechargeable

The electricity produced in batteries is described as direct current (dc).

Direct current fl ows in one direction and does not change direction.

Non-rechargeable batteriesA battery is made up of a number of cells. For example, the popular

AAA battery is a single cell (although we call it a battery) that supplies

1.5 V. The fl at PP3 is a battery that consists of six 1.5 V cells connected in Symbols for (a) a cell and (b) a battery.

P6

Activity A

Write down three appliances you have used today that are powered by batteries. Were the batteries rechargeable or non-rechargeable?

metal or

graphite

cathode

electrolyte

paste

paper or

cardboard

salt bridge

metal (often

zinc) anode

57


Cross-section of a dry cell.

series. It therefore supplies 9V. Non-rechargeable batteries contain what

are called dry cells. A dry cell is shown on the right.

A chemical reaction takes place between the electrolyte and the anode

which produces electrons at the anode. These electrons want to flow

towards the cathode where there aren’t many electrons, but the salt

bridge is in the way. When a wire is placed across the electrodes, the

electrons flow through it from the anode to the cathode generating

current. The chemicals are gradually used up, until there are none left to

produce charge. The battery then stops working.

We use non-rechargeable batteries for items that need little current,

such as remote controls, or for things that we don’t use often, such as an

emergency torch. These batteries are cheap and don’t lose their energy

(called self-discharge) as quickly as rechargeable batteries. However,

they do contain chemicals that are harmful to the environment if they go

into landfill.

Unit 16: See page xxx for information about making batteries.

Safety and hazards

Dead batteries must be disposed of safely. Some batteries contain toxic mercury that may leak into the environment. Leaking batteries may also cause burns if the acid inside comes into contact with skin. In some areas of the UK, all types of battery can be recycled.

Activity B

What kind of electricity is produced by a battery? Why does it have this name?

Rechargeable batteriesCells in rechargeable batteries are called secondary cells. These

batteries are mostly used in portable items that are used regularly, such

as mobile phones and laptop computers. The chemical is used up as

the battery is used, but in this case the process is reversible. The battery

can be recharged by applying an electric current to it, which reverses

the chemical reactions that take place during its use.

A rechargeable car battery.

1 Explain the difference between a rechargeable and a non-rechargeable battery. Give five examples of uses of each.

2 Draw a labelled diagram of a primary cell.

3 Discuss with a partner the advantages and disadvantages of rechargeable and non-rechargeable batteries.

Assessment activity 2.10 P6

P6P6

P6

P6

Grading tipTo meet part of the grading criterion for , make sure that you include a diagram for the primary cell. To get all of the criterion you need to also describe another way of generating electricity.

P6

boiler

heat

transformer

cooling tower national grid

turbinegenerator

58


2.11 Producing electrical energy – non-renewable sourcesIn this section:

Non-renewable energy sources –

energy source that we cannot replace,

for example, fossil fuels.

Mains electricity – electricity that

comes into our homes and places of

work. The voltage is normally 230V and

the frequency is 50Hz.

Key terms

Most power stations produce electricity by heating water to create

steam. This steam is used to turn turbines which then rotate a generator

to produce electricity. The electricity is then sent to our homes via the

national grid.

The water is often heated by non-renewable energy sources.

Fossil fuelsIn many power stations the non-renewable sources of energy are in

the form of fossil fuels: oil, coal or gas. The efficiency of most fossil fuel

power stations is only about 30%, although the efficiency of newer ones

may be as high as 50%. When fossil fuels burn, carbon dioxide (CO2) is

given off, which is a form of air pollution.

Unit 2: See page 46 for how efficiency is calculated.

Nuclear powerIn a nuclear power station, energy given out during nuclear reactions is

used to heat water to create the steam. No burning of fuel takes place.

Electricity generated by nuclear power plants does not create CO2 and

is relatively cheap to produce. It does produce radioactive waste.

Producing electricity – ac generatorsElectrical generators use induction to supply electricity. The turbine

that is turned by the steam created in the power station boilers then

rotates a generator which is a large coil of wire between magnets. The

magnetic field induces a current in the coil.

The diagrams on the next page show a simple ac (alternating current)

generator and the output produced (compared with a direct current).

Did you know?

In the UK, almost 79% of the electricity generated comes from fossil fuels and about 5% is generated by nuclear energy. Nuclear power stations are about 30% efficient – similar to those that use fossil fuels.

Safety and hazards

Nuclear power stations generate nuclear waste, which is radioactive. It is very dangerous and needs to be stored safely for thousands of years until it is no longer radioactive. People living near nuclear reactors also worry about radioactive leaks that may occur in the running of the plants.

Electricity generation and distribution.

P6 M4

steady rate of rotation

meter pointer swings

from side to side

alternating

voltageSN

brushesslip rings

coil

dc signal, sign is not

changing direction with time

ac signal, sign is changing

direction with time

Time (s)

Voltage

(V)

A simple ac generator.

59


The current generated by the coil is delivered to the circuit via springy

metal contacts called brushes which rest on the slip rings. The brushes

and slip rings allow constant contact with one side of the coil even

though it is rotating. The alternating current is due to the sides of the

coil moving through the magnetic field in opposite directions.

Activity A

Write down the name of the device that produces alternating current.

The mains electricity supply in our homes is an alternating current with

a frequency of 50Hz. This means the current changes direction 50 times

every second.

Output from ac and dc generator.

Case study: Let’s get efficient

Mary is a trainee engineer working for an electricity company. Part of her job involves investigating ways to make the electricity generators more efficient.

Make a list of all the areas in a power station where energy may be wasted and the ways that these losses may be reduced.

You must produce a report on nuclear power for an electricity company.

1 Draw a pie chart to show the percentages of electricity that are produced in the UK from fossil fuels and nuclear power.

2 Discuss with a partner the advantages and disadvantages of fossil fuel power and nuclear power. Which is more efficient and what are the effects on the environment? Put these arguments, along with your pie chart, into a report.


Grading tip

When you draw a pie chart, the total

must add up to 100%. You will need

to include electricity generated by

alternative methods, which you can

label as ‘Other’.

Functional skills

In discussing nuclear energy and fossil fuels as a way of producing electricity, you will develop both speaking and listening skills, as you present your arguments and listen to the views of others.

M4

P6

M4

P6

Activity B

List four ways that alternating current can be increased.

Science snippet

The current produced by an ac generator can be increased by:

using stronger magnetsrotating the coil faster increasing the number of turns of wire on the coilmaking the coil thicker.

60


2.12 Producing electrical energy – renewable sourcesIn this section:

Transformer – a device that changes the

voltage of an alternating current without

changing its frequency.

Key term

The previous pages describe non-renewable energy sources. We can

also generate electricity using natural energy such as solar power

from the sun, wind or water power. These sources are described as

renewable because they do not run out.

Hydroelectric powerHydroelectric power stations are one example of the use of renewable

energy sources. Water is stored behind a dam, often high up in the

mountains. The height of the reservoir provides a source of potential

energy. When the water is released and fl ows downhill, the potential

energy is converted to kinetic energy and the energy transfer turns

the turbines to generate electricity. Because no heating is required,

there is no pollution. Hydroelectric power is thought to be the most

effi cient method of generating electricity, with nearly 90% effi ciency.

Unit 2: Energy transformations are described on pages 38–39.

Did you know?

Most of Norway’s electricity is produced by hydroelectric power, possible because of all its lakes and mountains. In the UK, only about 5% of electricity is produced in this way.

Activity A

List the energy transformations that take place in a hydroelectric power station.

Building a hydroelectric power station is expensive and some people

are also concerned that they cause fl ooding and spoil the natural beauty

of the area.

Wind powerWind turbines use the kinetic energy of the wind to turn the turbines to

produce electricity. No pollution is produced, but people worry that the

wind turbines spoil the view of the countryside and about the noise the

turbines produce. Although wind is free, wind turbines are expensive to

set up and electricity generation depends on the wind – if there is no

wind, no electricity is generated. When they do operate, the effi ciency is

reported to be 35–60%.

Solar powerSolar power can be harnessed using solar cells called photovoltaic

cells. When the sun shines on these cells they emit electrons which

form a current. The solar panels are expensive, but the energy source

is free and no pollution is produced. However, the amount of electricity

generated depends on how bright the sunshine is. As with wind power,

the effi ciency of energy conversion varies. It is reported as 12–25%.

Hydroelectric power stations are expensive to build but cost little to run and do not cause any pollution.

D4M4P7P6

step-up

transformer

consumer

step-down

transformer

25 000V

40 000V

230V

power station

61


The national grid at work, showing transmission lines and transformers.

Activity B

Compare the efficiencies of three renewable methods used to generate electricity and list their advantages and disadvantages.

Getting electricity to our homes and factoriesThe UK has a network grid of pylon towers linked by copper cables that

transfer electrical energy to our homes. The voltage produced at the

power station is about 25000V. Engineers then increase this voltage to

400000V using a step-up transformer. Transferring electricity through

the national grid at a higher voltage reduces energy losses during the

transfer. The higher the voltage, the lower the current becomes so

the lower the energy loss. Using thick cables also reduces energy loss

because it decreases resistance.

Unit 2: Ohm’s law, which describes the relationship between

current and voltage, is described on page 55.

We use 230V mains in our homes and up to 11000V in some factories.

The voltage from the national grid is reduced using a step-down

transformer.

1 Describe why the voltage used in the home is different from that used to transmit electricity over the national grid.

2 Which equipment is used to increase and decrease the voltage as electricity is transferred from the power station to our homes and factories?

3 Which type of renewable energy power station would you recommend to be built near your community? Prepare a presentation that describes the advantages and disadvantages including the impact on the local environment.

Grading tipFor , ensure that you include each stage of electrical generation. Using a diagram will make your description clear. For consider the efficiencies for both non-renewable energy, such as fossil fuels or nuclear generation, and renewable energy, such as hydroelectric and solar power. For remember to include “consumer products” in the discussion. These are products such as TVs, washing machines etc.

Assessment activity 2.12 D4

P7

P7

D4

D4

M4

M4

D4

D4

M4P7

P7

62


2.13 Understanding our universeIn this section:

Orbit – the path of an object moving

through space, such as the path of the

Earth as it goes round the Sun.

Key term

Stars being born. Each small bulge will eventually form into a collection of planets the size of our Solar System.

The Solar SystemThe Solar System consists of the Sun and all objects that are attracted

to the Sun by gravity. These include the eight planets and other objects

such as asteroids and meteoroids. The Sun is the brightest star and is

the centre of the Solar System. It contains almost 99.9% of all the mass

in the Solar System. Because the Sun is so huge, its gravity holds the

planets in their orbits around it.

Objects in the night skyIf you look at a clear night sky, you will see that it is fi lled with various

objects. With the naked eye you can see the light of thousands of stars,

which seem to be arranged in patterns, called constellations. Because

the Earth rotates, the stars rise and set like the Sun. You will also see

planets. These don’t shine their own light but refl ect light from other

sources, such as the Sun. Because they are close to the Earth, they shine

brightly and do not twinkle like stars.

If you are lucky you may see an object with a bright tail. This is likely to

be a comet. Comets are made from rock, dried ice and frozen gases

such as carbon dioxide and methane. They come from outside our Solar

System. You may also see ‘shooting stars’, which are meteors. These

are bits of dust and rock that enter the Earth’s atmosphere. Astronomers

have also discovered hundreds of stony objects called asteroids, which

are also in orbit around the Sun.

Did you know?

Stars are so far away that their distances from us are measured in ‘light years’. As the name suggests, a light year is the distance travelled by light in 1 year. Light travels 300 million metres in 1 second so a light year is about 1013 kilometres.

Case study

Probing Near-Earth Objects (NEOs)

Rachael is a technician at the European Space Agency. She is part of a group of scientists and engineers who are designing the next generation of space probes. Some of these probes will be used to collect samples from space objects close to the Earth, for example asteroids and comets.

What could we learn from analysing

these samples?

P9

Sun

Asteroids

Comet

Mercury

Venus

Earth

Mars

Jupiter

Saturn

Uranus

Neptune

Pluto

63


Activity A

Which objects in the night sky don’t shine with their own light?

The Earth’s moon is clearly visible and its appearance changes through

the month as it orbits the Earth. With a good telescope you can see that

other planets also have moons. Jupiter has 63 moons. One of these,

called Io, has active volcanoes on its surface.

Origin of the Solar SystemAstronomers believe that the Solar System was formed when clouds

of gas and dust collided, because of some sort of explosion that

happened in space. Eventually our Sun was formed, together with other

objects such as planets. Asteroids and meteoroids are believed to be

the remains of that cloud.

Geologists have investigated meteorites (meteors that have landed

on Earth) and estimate they are 4.5 billion years old. The effect of

meteoroids and asteroids that hit the surface of the moon is clearly seen

as craters, even with the naked eye. Some astrophysicists believe that

the Earth was formed by collisions of asteroids and meteoroids.

The solar system is made up of the Sun, eight planets, the dwarf planet Pluto, asteroids and comets. Previously Pluto was thought to be a planet.

You are an astronomer working for an observatory. You are invited to a primary school to describe our Solar System to young children.

1 Working in groups of three, construct a model of the Solar System showing the distances of the eight planets from the Sun.

2 In your groups, investigate the theory described above of how the Solar System was formed. Present your results in the form of a poster.

Grading tipFor : When describing the Solar System, make sure you include objects other than planets; there are many other objects out there apart from planets.


PLTS

Producing a model of the solar system will develop your creative skills and presenting your work will help you develop team skills.

P9

P9

P9

2.14 Understanding our universe – how did it all happen?

In this section:

Red shift – light from stars that

are travelling away from us comes

from closer to the red end of the

electromagnetic spectrum than light

from the Sun.

Big Bang theory – the theory that the

Universe began with an explosion.

Cosmic background radiation –

electromagnetic energy that comes from

all directions in space and is predicted

to have come from the Big Bang.

Key terms

The Universe is made up of many different objects.

Our Milky Way galaxy: its shape is a spiral and the Sun is near the edge, as shown in this representation.

Our UniverseSo far we have looked at our Solar System, but our Sun is not the only

star in the region. It is one of about 100 billion stars in our galaxy, which

is called the Milky Way. The Milky Way is a spinning spiral disc. On a

clear dark night without any pollution or street lights, you can see it as a

‘milkyish’ light band.

Our Solar System is on the edge of the Milky Way. It takes about 220

million years for our Solar System to orbit the Milky Way, even though it

is estimated to be travelling at 100 000 miles per hour. This means that it

has just completed one orbit since the fi rst creatures appeared on Earth.

Our galaxy is the second largest in a group of seventeen galaxies. The

nearest galaxy to the Milky Way is called M31, the Andromeda galaxy.

Beyond this are other clusters of galaxies, with their own stars and

planets. These clusters form a shape which is a little like a honeycomb.

All these clusters make up what we call the Universe. Astronomers

believe that there are about 100 billion galaxies in the Universe.

Activity A

What is the name of our galaxy? Name one other galaxy.


64

P10 M5 M6 D5 D6


P10

M6D6

M5 D5

65

Expansion of the UniverseMany astrophysicists believe that the Universe is expanding. You can

imagine this as bread with raisins in it rising: the raisins represent the

galaxies, moving away from each other as the bread rises. Light coming

from galaxies has provided evidence for this expansion.

Light forms a spectrum of wavelength and frequency. The visible part

of the spectrum starts with violet and ends with red. The further you go

towards red, the longer the wavelength.

Astrophysicists have found that light coming from distant galaxies is

shifted towards the red end of the spectrum. The more distant the

galaxy, the bigger the shift is. They call this a red shift. (It is also known

as the Doppler effect.) A possible explanation for this red shift is that

the galaxies are moving away from us. This suggests that the Universe

is expanding.

Unit 2: The electromagnetic spectrum is described on pages 50–51.

The Big Bang theoryAccording to the Big Bang theory, galaxies and indeed the Universe

were once a fixed point that then exploded. The theory also suggests

that radiation was given off during this explosion, and that this

radiation should still be detected today. This radiation is called

cosmic background radiation and it was detected in the 1960s. NASA

confirmed this discovery in 1992, using its newly built satellite called

Cosmic Background Explorer (COBE).

So what next for the Universe? Cosmologists believe that the Universe

could follow one of the following paths.

It could continue to expand for ever.

The expansion will slow down, but won’t quite stop.

The expansion could come to a complete stop, forming a massive

black hole (singularity).

Unit 18: See page xxx for more information about black holes.

Did you know?

In the centre of our galaxy (the Milky Way) there is a black hole that is 4 million times bigger than our Sun.

You are being interviewed for a job at a space technology company. You must produce a presentation on space. In your presentation:

1 List the evidence that suggests that the Universe is changing.

2 Describe the evidence that indicates that the Universe is changing.

3 Describe the strengths and weaknesses of this evidence.

4 Describe the Big Bang theory of how the Universe was formed ; how sure are you that this theory is correct?

Assessment activity 2.14 Grading tip

To obtain , make sure you include

the red shift and the COBE as evidence

that the universe is expanding. In

attempting , remember that you

need to describe how the evidence

you identified for suggests a

changing universe. For you

need to discuss the evidence for and

against stating that the universe

is changing.

D6M5 D5P10 M6

P10

M6

D6P10

Activity B

What does the Doppler effect tell us about our Universe?

Just checking

Assignment tips

1. What is the difference between rechargeable and non-rechargeable batteries?

2. With the aid of a diagram, describe how an ac electrical generator works. Sketch a graph showing

the electrical current that is produced.

3. Sketch the current provided by dc supply.

4. Describe how electricity is brought to our homes.

5. List three ways that heat is lost from a house.

7. What is the name of our galaxy?

8. How many planets are there in our Solar System? Name these planets.

9. Name three types of radiation and give an application of each.

To get the grade you deserve in your assignments remember the following.

Make sure that your assignments are written as clearly as possible. Always read them through when you

have fi nished.

Make sure that, when you plan experiments, you have thought about what kind of results you expect to

get and have prepared a table for them. What kind of apparatus is likely to be available? Make sure you

plan well, allowing yourself plenty of time.

Don’t forget to include the correct units when solving numerical problems. Always check your calcula-

tions before you hand in your work for assessment.

Some of the key information you’ll need to remember includes the following.

Knowing the difference between energy block diagrams and Sankey diagrams – remember the width of

each arrow in a Sankey diagram corresponds to the value of the energy transferred.

Knowing the difference between ionising and non-ionising radiation – remember ionising radiation

knocks electrons out of the atoms it comes into contact with.

When doing work on the electromagnetic spectrum, remember the smaller a wavelength is, the higher

the frequency.

Renewable sources of energy are those that don’t run out, for example wind energy and solar energy.

Non-renewable sources of energy are ones that will run out, for example fossil fuels and nuclear fuels.

You may fi nd the following websites useful as you work through this unit.

For information on… Visit…

the different types of energy, its transfer and uses http://www.gcse.com/energy.htm

the full range of electricity generation technology http://www.electricitygeneration.co.uk

energy-saving measures http://www.energysavingtrust.org.uk

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